Studies were continued on clostridial glycine reductase that catalyzes the reductive deamination of glycine and the concomitant synthesis of ATP. The protein C component, isolated in apparently homogeneous form, behaves as an associating-dissociating system of two dissimilar subunits. Marked loss of activity using certain types of chromatographic steps (e.g., hydroxyapatite) seems to be due to selective loss of one of the subunits. The catalytic activity of protein C is destroyed by alkylation and by brief heating at 50 degrees C. Scale-up of the isolation procedure for protein C is in progress and antibodies will be produced to be used for studies on regulation of its biosynthesis. To study the mechanism of insertion of the selenocysteine residue in the selenoprotein A of glycine reductase, experiments have been initiated to isolate and clone the cDNA encoding this selenoprotein. Comparison of the DNA sequence with the known sequence of a 16-residue selenocysteine containing peptide isolated from selenoprotein A should provide information concerning a putative precursor amino acid. The collaborative program with A. Bock of Munchen on the origin of the selenocysteine residue in a formate dehydrogenase of E. coli took a very interesting turn when the Munchen group found that a stop codon within the cDNA that codes for this protein is suppressed and read-through occurs. This stop codon is within the DNA sequence corresponding to a large selenocysteine containing peptide located near the amino terminus of the selenoprotein subunit of the enzyme. The stop codon may be used here to specify selenocysteine insertion by some unknown mechanism. We have developed procedures for isolation of labeled peptides generated by treatment of 75-Se-labeled formate dehydrogenase with specific proteases. Scale-up of these methods is in progress in order to obtain sufficient amounts of the highly hydrophobic selenocysteine containing peptide(s) for amino acid sequence analysis. A method for isolation of pure amino acid transfer ribonucleic acids (tRNAs) was further developed using a monoclonal anti-AMP antibody affinity column obtained from Dr. Sue Goo Rhee. This procedure proved to be far superior to previous methods using a boronate affinity column matrix.